間接接合型鋼框架斜撐在鋼筋混凝土構架耐震補強之應用

Application of Steel Frame Bracing System with Indirect Connection on Seismic Retrofit of RC Frame

楊季軒(Chi-Hsuan Yang)

指導教授 ： 黃世建

國立臺灣大學/工學院/土木工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.01851

摘要

在國內針對既存建築物的補強是非常重要，本研究採取間接接合型式之鋼框架斜撐補強工法，增加既有鋼筋混凝土構架之垂直承載力及側力強度，期望補強強度能介於磚牆補強與RC剪力牆補強之間，並能保有足夠之變形能力。參考日本耐震改修設計指針，設計六座實尺寸補強試體進行側向反覆載重測試。
根據實驗之結果，補強接合部角隅處為傳遞力量之重要角色，若此區域開始開裂、擠碎，補強構架之強度將無法繼續發展或維持。第一階段補強試體藉縮小螺旋箍筋間距及採用強度較高之無收縮砂漿，對於界面圍束效果及強度有明顯的提升。不過因角落應力集中導致砂漿嚴重開裂、強度大幅衰減，雖有很高的補強強度，但變形、韌性不足，鋼斜撐及RC構架強度無法有效發揮。第二階段補強試體採用隅板作為鋼斜撐與鋼框架之接合，可避免角落應力集中、使斜撐力量分散，角落未明顯破壞，補強各構件強度均能有效發揮及均衡發展，不僅有足夠之補強強度，變形及韌性也相當良好。此外，縮小鋼斜撐尺寸、降低補強倍率可增加補強試體之變形能力，將補強倍率定義為補強後強度與純構架強度之比值，本研究7倍補強倍率之變形能力僅為1%、5.5倍則可提升為2%、4倍則可到達3%。參考校舍一般柱之最大強度發生在2~3%，為使既有結構強度有效發揮，評估本補強研究之RC構架適合之補強倍率為4倍，可作為校舍補強之參考。
對於補強設計流程之建議，先考量補強現地結構尺寸、混凝土強度，配置容許之錨栓尺寸、間距及埋深，計算錨栓可提供之剪力強度，再選擇側向強度低於錨栓之鋼斜撐及設計隅板，並可由此控制補強構架之補強倍率，避免補強接合部強度低於鋼斜撐造成構架強度無法有效發揮之情形，最後可利用標稱剪力強度檢核既有構架承載能力。

關鍵字

耐震補強 ； 鋼筋混凝土構架 ； 鋼框架斜撐 ； 隅板 ； 補強接合部 ； 變形能力

並列摘要

It is very important to retrofit exsiting RC buildings in Taiwan. This study used steel frame bracing system with indirect connection to enhance the vertical bearing capacity and lateral strength of RC frames. It is expected that the retrofitted frame can possess strength between brick walls and shear walls and have adequate deformation capacity as well. This study tested six full-scale retrofitted specimens which were design according to Japan Standard and Guildelines for Seismic Evaluation of Existing Reinforced Concrete Buildings.
According to the test results, the corner joints of the mortar connection played an important role for transferring force and maintaining strength. The lateral strength of phase-I specimens can be improved significantly by closely spaced spiral reinforcement and high strength non-shrinkage mortar. However, the morter cracked and strength decreased quickly due to the stress concentration at the corner joints. Although the phase-I specimens exhibited higher strength, however deformation capacity is rather poor. Moreover, the material strength of steel brace and RC frame was not effectively developed. The phase-II specimens employed gusset plate to distribute the brace forces and to avoid stress concentrate at corner. The corner joints of the mortar connection were preserved before peak load. Thus, the retrofitted frame had adequate lateral strength, deformation capacity and ductility. In addition, the use of smaller steel brace can increase the deformation capacity of specimens. The retrofitting ratio is defined as the ratio of retrofitted strength relative to original strength. In this study, deformation capacity is only 1% with the retrofitting ratio of 7, 2% with the retrofitting ratio of 5.5, and 3% with that of 4. As an indicator for school buildings using this retrofitting method, the retrofitting ratio of 4 seems to be an adequate choice. Because the maximum strength of typical columns of school buildings were achieved at lateral drift of 2 to 3%, a deformation capacity of 3% for retrofitted frame is appealing.
The design procedure of this retrofitting scheme is suggested as follow. First step is to select the anchors base on the limitations of existing frame. According to the capacity of anchors, the size of braces can be determined. The gusset plate is then designed accordingly. Finally, the column shear capacity of the existing RC frame is checked for safety.

並列關鍵字

seismic retrofit ； reinforced concrete frame ； steel frame bracing system ； gusset plate ； mortar connection ； deformation capacity

參考文獻

[3] 林叡延，「補強用鋼框架斜撐與既有RC構架之接合研究」，碩士論文，國立台灣大學土木工程系，台北，民國102年7月，140頁。

[14] 蔡克銓、吳安傑、林保均、魏志毓與莊明介，2012，「槽接式挫屈束制支撐與脫層材料性能研究」，結構工程，第二十七卷，第三期，第29-59頁。

[27] 江文卿、邱聰智、蕭輔沛、杜怡萱、簡文郁、葉勇凱、鍾立來、黃世建，「花蓮縣新城國中校舍現地實驗－靜態單向側推」，國家地震工程研究中心，NCREE-08-008，台北，2008，296頁。

[5] AISC 360-10, “Specification for Structural Steel Buildings,” American Institute of Steel Construction (AISC), Chicago, Illinois., 2010.

[6] AISC 341-10, “Seismic Provisions for Structural Steel Buildings,” American Institute of Steel Construction (AISC), Chicago, Illinois., 2010.